The inhibition properties of two 3,5-bis (disubstituted)-4-amino-1, 2,4-triazole derivatives, namely 3,5-bis(4-methoxyphenyl)-4-amino-1,2,4-triazole (T1) and 3,5-bis(4-chlorophenyl)-4-amino-1,2,4-triazole (T2) were investigated for mild steel corrosion in 2 M H3PO4 medium at 308 K using electrochemical impedance spectroscopy (EIS), Tafel polarization curves and weight loss measurements. The results showed that the 4-amino-1, 2,4-triazole derivatives (T1 and T2) were good inhibitors in 2 M H3PO4, and the inhibition efficiency, η(%), increased with the inhibitor concentration but the temperature had no effect on the inhibition efficiency. The adsorption of T1 and T2 on the mild steel surface obeyed Langmuir's adsorption isotherm. Both thermodynamic and kinetic parameters were calculated and discussed. Data obtained from EIS studies were analysed to model inhibition process through appropriate equivalent circuit model. Potentiodynamic polarization curves revealed that T1 and T2 behave as mixed-type inhibitors. The adsorption behaviour of the 4-amino-1, 2,4-triazole derivatives on Fe (110) surface was investigated by Monte Carlo simulations in the presence of water to verify their corrosion inhibition efficacies. The results indicated that the adsorption energy of T1 was greater than T2, which is in accordance with the experimentally determined inhibition efficiency.